This invention relates in general to blood gas analyzers, and in particular, it relates to a device for and a method of assuring that the results obtained from a blood gas analyzer meet a quality control standard.
Blood gas analyzers are becoming increasingly important as analytical tools in medical laboratories. Blood gas analyzers typically measure the partial pressure of oxygen and carbon dioxide gases (P.sub.O.sbsb.2 and P.sub.CO.sbsb.2) found in blood samples. These measurements, along with a ph measurement of the blood sample, provide an accurate determination of the body's metabolism and thus provide a monitor of the patient's cardiopulmonary system.
Blood gas analyzers provide the attending physician with important information so long as the results obtained therefrom are accurate. However, the obtaining of accurate results may be extremely difficult with these devices since the gas content of the blood sample can be affected by atmospheric pressure and ambient temperature. Accordingly, the particular collection and analytical techniques employed by the laboratory must be precisely controlled. For example, blood samples retrieved from the patient must be isolated from the ambient and a constant temperature must be adequately maintained.
For a discussion of the clinical techniques employed to insure accurate blood gas analysis, see the article entitled "Reliable Blood Gas Analysis", Antonias L. van Kessel, American Society of Clinical Pathologists, Issue No. 20, 1975.
To insure that a blood gas analyzer is operating properly, it is usually frequently calibrated, at least on a daily basis. By calibration is meant a check and possible adjustment and readjustment of the blood gas analyzer to insure that the analyzer output accurately reflects the oxygen and carbon dioxide pressures of the sample at the measuring probe of the instrument. For a discussion of the calibration of blood gas analyzers, see the article entitled "Calibration of Blood Gas Analyzers" by Allen H. Runck, Proceedings of a Workshop on Ph and Blood Gases held at the National Bureau of Standards, Gaithersburg, Md., July 7 and 8, 1975, National Bureau of Standards, Special Publication No. 450.
However, even if a blood gas analyzer is properly calibrated, the results obtained therefrom, may not properly reflect the patient's condition. For example, if a batch of samples had been exposed to the ambient atmosphere, the blood gas analyzer may accurately determine the gas pressure of the sample, but this may not reflect the gas pressure of the patient's blood stream. Or, for example, sensor electrodes in the instrument may not be at the proper, i.e. body, temperature. Accordingly, a need exists, for not only calibrating blood gas analyzers, but also for subjecting the results of those analyzers to a quality control check. For discussion of the long felt need for quality control in blood gas analysis, see articles by Sorensen, Malenfant, Gambino and Noonan from the aforementioned Proceedings of a Workshop on ph and Blood Gases held at the National Bureau Standards, Gaithersburg, Md., July 7 and 8, 1975, National Bureau of Standards, Special Publication 450.
Of these articles the Sorensen and Malenfant articles indicate that tonometry is the preferred method of quality control in blood gas analysis due to its accuracy. However, tonometry is a relatively time consuming procedure, and, as pointed in the Noonan article, tedious and complicated quality control measures are ineffective since they are not utilized in busy laboratories. Accordingly, Noonan and Gambino recognize the desirability of what might be referred to as the ampoule or vial method of quality control in blood gas analysis.
In the ampoule or vial method of quality control, a sealed glass ampoule or vial is provided containing a reagent having a known quantity of gas dissolved therein. The reagent may, for example, be a buffered bicarbonate solution or whole blood. In any event, the contents of different vials are periodically inserted into the blood gas analyzer and the results are recorded. These results are compared against results obtained from earlier sampled standard vials. If the results obtained from a number of standard vials are consistently different from one another, it may be determined that a source of error has been introduced.
One problem which has been associated with the ampoule or vial method of quality control in blood gas analyzers has been that each ampoule or vial is capable of only a single use, for the reason that each time an ampoule or vial is opened, the contents thereof are exposed to the atmosphere and the partial pressure of the oxygen and carbon dioxide dissolved in the reagent contained therein begins to change. Because each ampoule or vial is capable of only a single use, the expense of packaging and employing these ampoules or vials is great.
Another problem associated with presently available ampoules is the fact that the reagent stored therein is found in both a liquid and a gas phase. At any particular temperature, the reagent in the ampoule will attain equilibrium between the liquid and gas phases. However, as the temperature of the vials change, the amount of gas dissolved in the reagent also changes. Therefore, before such vials are utilized, it is necessary to ensure that the vial is at a standard temperature. Many times this precaution is not taken in busy laboratories, thus reducing the effectiveness of a quality control effort.
It would be desirable to provide a device for and a method of calibrating a blood gas analyzer and for subjecting the results obtained from that blood gas analyzer to a quality control test which is both faster and more easily utilized than the aforementioned tonometry method and yet which is more economical than the ampoule method of quality control.
It would also be desirable to provide a device for and a method of quality control which would also be useful for calibration of blood gas analyzers.
Additionally, it would be desirable to provide a device for storing a reagent for use in the quality control of a blood gas analyzer which is unaffected by ambient temperature.
These objectives have been achieved in the present invention by the provision of a device for storing a liquid quality control reagent for use in a blood gas analyzer which comprises a first container of variable volume having a reagent contained therein which is exclusively in the liquid phase. An exit passageway is provided emanating from that container and a valve is situated in the passageway. The first container is situated in a second container and the space between the containers is filled with a compressed gas. Opening of the aforementioned valve allows for the release of the liquid quality control reagent either directly into the blood gas analyzer or into a syringe from which the reagent is then transferred into the blood gas analyzer.
Since the reagent is stored entirely in the liquid phase in the first container, the composition of the liquid reagent is unaffected by ambient temperature. Further, since the reagent is expelled by means of compressed gas which deforms the first container upon opening the valve, the device of the present invention is reusable in that the contents of the container are not exposed to the ambient. Accordingly, a number of quality control tests may be accomplished with a single filled device. Since the device is reusable, the expense of separately packaged vials is avoided and the possibility that the reagent concentration might vary from vial to vial is eliminated.
Also disclosed herein is a method of storing a liquid quality control reagent for use in the blood gas analyzer which comprises the steps of providing the aforementioned first container for receiving the liquid quality control reagent therein, the container having an input port projecting therefrom. Subsequently, the first container is overfilled with the reagent such that the liquid level in the container extends into the input port. The container is then sealed at the input port but below the liquid level and finally the container is externally pressurized. The employment of this method allows for the storing of liquid quality control reagent entirely in the liquid phase thereby preventing variation in the reagent parameters with temperature.